What is wrong with my heart and lung?

You probably bruised something the other day and then aggravated it again today without realizing it. I've been smoking since I was 14, now 50,(wish I didn't but that's another story) and usually if you're having trouble taking a deep breath it will be both lungs not just one side. By not being able to take a deep breath and it only hurts on one side sounds like a bruise. If not better in a couple days head to urgent care and let them check you out. You may have even cracked a rib.